The overall goal of this application is to ascertain the mechanism of GnRH induction of immediate-early genes in the pituitary gonadotrope and determine their role in pulsatile GnRH regulation of the gonadotropin beta-subunit expression. Gonadotropin beta-subunit genes are specifically expressed in the anterior pituitary gonadotrope in response to GnRH pulses from the hypothalamus. They are the limiting factors in synthesis of the heterodimeric glycoproteins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Their differential expression throughout the menstrual cycle is critical for reproductive function. Herein, we utilize novel approaches to delineate the mechanisms underlying their differential expression. We propose to analyze the expression and regulation of the immediate-early genes, c-Fos and Egr-1, that are activated by GnRH to induce expression of gonadotropin beta genes. In the three aims of this proposal, we will compare and contrast the expression of these immediate-early genes to elucidate the molecular mechanisms of their induction and their roles in differential expression of the LH versus FSH beta-subunit genes. In the first aim, we will determine optimal GnRH pulse frequency or amplitude for maximal expression of Egr-1 and LH beta versus the expression of c-Fos and FSH beta. In the second and third aims, we will analyze the signal transduction pathways activated by GnRH that are implicated in the expression of the immediate-early genes, with a special emphasis on physiologic pulsatile GnRH. Results obtained from this R03 proposal will make substantial contributions to our understanding of the molecular mechanisms that affect gene expression in the gonadotrope and provide insight into the physiology and pathophysiology of the mammalian reproductive system. A long-term goal of this application is to provide key results to establish an independent research program building on the PI's previous accomplishments in gonadotropin-releasing hormone (GnRH) regulation of gonadotropin gene expression and develop an R01 application. This future R01 will propose to expand our understanding of GnRH regulation of gene expression in the pituitary using genomics, the mechanisms of GnRH induction of immediate-early genes in the gonadotrope, and the function of these genes in vivo, utilizing genetically modified mice. Fertility in mammals is regulated by the integration of different regulatory signals that occurs at the level of the gonadotrope cell population in the pituitary gland, through modulation of gonadotropin gene expression and secretion. Dysfunction at the level of gonadotrope gene expression can lead to pathophysiologic disorders such as infertility, precocious puberty, polycystic ovarian syndrome, and hypogonadotropic hypogonadism. Thus, understanding the molecular mechanisms governing gonadotrope gene expression will lead to insight into the physiology and pathophysiology of the reproductive system.